The present invention relates to an apparatus for manufacturing paper pipes, and more particularly to an apparatus for manufacturing paper pipes in which a paper tape or tapes are wrapped spirally around a mandrel by means of two belts in such a manner that one longitudinal edge of the paper tape overlaps the other longitudinal edge.
The optimum angles at which the paper tape or tapes should be wrapped spirally around the mandrel differ with the breadth of the paper tape, the diameter of the paper pipe to be manufactured, and the purpose for which the paper pipe is going to be used. For this reason, it is desirable in an apparatus of this kind that the angles formed by the two belts with the mandrel can be adjusted in accordance with the angle at which the paper tape or tapes are going to be wrapped spirally around the mandrel.
Conventional apparatuses of this kind can be divided broadly into two types. One type of the conventional apparatuses includes a single driven drum provided on one side of a mandrel, two driving drums provided on the other side of the mandrel, and two belts which are adapted to operate over the driving and driven drums in a V-shaped arrangement with the driven drum as the vertex. The other type of the conventional apparatuses includes two driving drums provided on one side of a mandrel, two driven drums provided on the other side of the mandrel, and two belts which are adapted to operate over the driving and driven drums in substantially parallel arrangement. In both types of conventional apparatuses, the tight side of each belt winds round the mandrel so that the belt will form a single loop around the mandrel.
In the first type of the conventional apparatuses, the angle formed by the two belts is only slightly adjustable and, consequently, the angle at which the paper tape or tapes are wrapped spirally around the mandrel can be changed only within narrow limits. This drawback makes the first type of the conventional apparatuses unfit for the manufacture of paper pipes other than specific ones.
Another drawback of the first type of the conventional apparatuses is that, because of its intricate and weak structure, the paper tape or tapes cannot be tightly wound round the mandrel. In this connection, it should be borne in mind that the belt tension has a great influence on the strength of paper pipes. In order to obtain a strong paper pipe, it is necessary to strain the belts as much as possible.
In the second type of the conventional apparatuses, too, the angle formed by the two belts is only slightly adjustable. In addition, because a large space is left between the loops formed by the two belts around the mandrel, the mandrel is apt to undergo deflection and the paper tape or tapes cannot be tightly wound around the mandrel in this type of the conventional apparatuses either.
Still another drawback which is common to both types of the conventional apparatuses is that the belts are apt to slip on the driving drums, because not all the drums are adapted to transmit the driving power of the motor to the belts.